This invention relates generally to particle detectors. A particle is defined herein as any agglomeration of matter. Particles can include, for example, atomic species, molecular species, viruses, biological cells, and nanotubes. There are numerous types of particle detectors known in the art. One type of charged particle detector is an optical detector that uses a light beam, such as a laser, to scatter light from the particles, thereby generating a photocurrent at a detector. The resulting photocurrent waveforms are then analyzed to obtain the particle size information. The scattering cross section of particles is a function of the wavelength of the analyzing light beam. Particle detectors using light beams generally can only detect particles that are over about 100 nm because of wavelength limitations. See, for example, U.S. Pat. Nos. 5,835,211 and 6,784,990 for a description of particle detection based on laser scattering and laser light extinction.
Another type of particle detector is a condensation particle detector. Condensation particle detectors can be used to detect particles with dimensions below 100 nm. Particles this small act as nucleation sites for condensation of liquid droplets. The liquid droplets are of a sufficient size that can be easily detected with a light beam or other detection means. However, condensation particle detectors do not provide any information on the particle size.
Another type of particle detector is a time-of-flight particle detector. Time-of-flight particle detectors measure particles arriving at the detector as a function of time. The mass of a particle can be determined by measuring the time it takes a particle to be detected after passing through a known electric field. See for example, U.S. Pat. No. 6,553,849 for a description of time-of-flight (TOF) particle detector.